Apparatus for monitoring reproduced audio signals during fast playback operation

Abstract

Apparatus for monitoring reproduced audio signals during fast playback operation comprises a bucket-brigade device for storing pieces of audio information reproduced from a recording medium at a high speed. The stored pieces of information are read out in a sequence at a slower speed than they were stored when the magnitude of the reproduced audio signal exceeds a predetermined value so that the audio information will be restored to the original pitch to be monitored. The interval for which an audio signal is stored in the bucket-brigade device may be controlled in accordance with the speed of the recording medium.

What is claimed is: 
     
       1. Apparatus for monitoring reproduced audio signals during fast playback operation, comprising: (a) a first pulse generator for producing a first pulse train signal;   (b) a level detecting circuit responsive to a reproduced audio signal for producing an output signal when the magnitude of said reproduced audio signal exceeds a predetermined value;   (c) a memory circuit for storing pieces of said reproduced audio signal in a sequence in response to said first pulse train signal;   (d) a second pulse generator for producing a second pulse train signal the frequency of which is much lower than that of said first pulse train signal;   (e) a switching circuit for selectively supplying said memory circuit with one of said first and second pulse train signals;   (f) a control circuit responsive to said output signal of said level detecting circuit for controlling said switching circuit, said switching circuit being controlled to supply said memory circuit with said second pulse train signal upon presence of said output signal of said level detecting circuit so that said pieces of information prestored in said memory circuit are read out at a normal pitch.   
     
     
       2. Apparatus as claimed in claim 1, further comprises means for producing a signal indicative of the speed of a recording medium on which said audio signal was recorded, and wherein said first pulse generator comprises a variable-frequency oscillator the oscillating frequency of which varies in accordance with said signal indicative of said speed. 
     
     
       3. Apparatus as claimed in claim 2, wherein said variable-frequency oscillator comprises a voltage-controlled oscillator. 
     
     
       4. Apparatus as claimed in claim 3, wherein said voltage-controlled oscillator is responsive to a voltage applied to a drive motor which drives a take-up reel of a tape player. 
     
     
       5. Apparatus as claimed in claim 1, wherein said level detecting circuit comprises an envelope detector responsive to said reproduced audio signal, and a comparator responsive to an output signal of said envelope detector. 
     
     
       6. Apparatus as claimed in claim 1, wherein said memory circuit comprises a bucket-brigade device. 
     
     
       7. Apparatus as claimed in claim 1, wherein said control circuit comprises a microcomputer, and wherein said second pulse generator is a clock pulse generator built in said microcomputer. 
     
     
       8. Apparatus as claimed in claim 2, further comprises an A/D converter responsive to said signal indicative of said speed, said A/D converter supplying said control circuit with a digital signal indicative of said speed so that said control circuit controls said switching circuit such that said first pulse train signal is fed to said memory circuit for a period of time which is proportional to a reciprocal of said speed. 
     
     
       9. Apparatus as claimed in claim 8, wherein said control circuit is so constructed that it controls said switching circuit such that said second pulse train signal is fed to said memory circuit for a period of time required to read out all information stored therein. 
     
     
       10. Apparatus as claimed in claim 1, further comprises a gate circuit for passing the output signal of said memory circuit only when said switching circuit passes said second pulse train signal. 
     
     
       11. A method of monitoring reproduced audio signals during fast playback operation, comprising the steps of: (a) reproducing an audio signal from a recording medium at a speed higher than it was recorded;   (b) detecting the magnitude of the reproduced audio signal;   (c) producing a first pulse train signal;   (d) storing said audio signal in a memory circuit in accordance with said first pulse train signal;   (e) producing a second pulse train singal having a frequency higher than that of said first pulse train signal;   (f) supplying said memory circuit with said second pulse train signal when the magnitude of said reproduced audio signal is detected to be above a predetermined value, for reading out the audio signal prestored in said memory circuit at a normal pitch.   
     
     
       12. A method as claimed in claim 11, further comprising the step of varying the frequency of said first pulse train signal in accordance with the speed of said recording medium. 
     
     
       13. A method as claimed in claim 11, further comprising the step of determining an interval, for which said audio signal is stored in said memory circuit, in view of the speed of said recording medium and the capacity of said memory circuit. 
     
     
       14. A method as claimed in claim 13, further comprising the step of determining an interval, for which said audio signal prestored in said memory circuit is read out, such that all information stored in said memory circuit can be read out by said second pulse train signal. 
     
     
       15. A method as claimed in claim 11, further comprising the step of passing the output signal of said memory circuit only when said second pulse train signal is applied to said memory circuit.